The aim of this research is to define the mechanism of protein synthesis regulation by double-stranded RNA as related to the functional expression of (2'-5')An (a series of unique oligonucleotides consisting of 5'-adenylic acid residues joined by a 2'-5' phosphodiester linkage) in lysed rabbit reticulocytes. Specifically, we intend to test the hypothesis that the function of (2'-5')An is not limited to its activation of a dormant endonuclease activity, but includes its specific interaction with other factors localized in the 0.5 M KCl ribosomal wash. This hypothesis will be tested as follows. First, the specificity of (2'-5')An-activated endonuclease will be studied using mRNA which has been structurally modified with specific enzymes. Second, other possible functions of (2'-5')An will be investigated by studying the profile of radioactive (2'-5')An association with macromolecules. Results from this study should further advance our knowledge of the functions of (2'-5')An in translational control and in the establishment of antiviral state in interferon-treated mammalian cells.